Maintenance of the Joint European Torus (JET) reactor led to generation of soft housekeeping materials contaminated with tritium and comprising various polymeric materials. Some of the wastes fall into the category of intermediate-level waste and require processing to reduce the volume and/or change the category to low-level waste. Plasma arc centrifuge (PAC) combustion and countercurrent regime of gasification have been studied as candidates for a future waste treatment facility for JET tritium-contaminated wastes. This study was carried out for JET wastes that did not contain tritium. Mass reduction factors from 8 to 46 and from 35 to 143 for countercurrent regime of gasification and PAC combustion, respectively, have been demonstrated to be dependent on waste composition. Volume reduction factors from 20 to 100 and from 95 to 400 for countercurrent regime of gasification and PAC combustion, respectively, have been also estimated to be dependent on waste composition. The wastes and combustion products including chlorine-containing combustion products have been characterized using standard procedures and various analytical procedures developed for this study. The formation of water as a secondary waste was estimated for countercurrent regime of gasification, which was important for the ultimate processing of tritium-contaminated wastes.